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172 MORPHOLOGY AND EVOLUTION
The hyo-glossus <fig. Slu) arises from the body and great cornu of the hyoid bone; and the fibres pass upwards to the side of the posterior half of the tongue under the stylo-glossus. It is not fused with its neighbour, but fibres from the thyro-hyoid pass into it in the Chimpanzee. The relations are as in Man.
The stylo-glossus .sfig. 31r>) arises from the base of the styloid process, or from the styloid area of the skull when no process is present. It is inserted into the side of the tongue from the base to near the apex. Its anterior part is concealed by the sublingual gland, with the lingual nerve encircling its posterior border. Wharton's duct crosses it obliquely from behind forwards, and the communication between the lingual and hypoglossal nerves runs downwards and backwards over it anteriorly.
The superior constrictor of the pharynx in the Chimpanzee is continuous above with the buccinator. It is attached to the mylo-hyoid line on the mandible, the internal pterygoid plate, the base of the tongue, the mucous membrane of the floor of the mouth, and the bucco-pharyngeal aponeurosis. Its lower border is overlapped by the middle constrictor of the pharynx, and the stylo-pharyngeus passes between them after sending some fibres into the superior constrictor. The sinus of Morgagni is large, but the tensor and levator palati which are contained within it are more horizontal than in Man. The constrictor is attached above and behind to the basis cranii. A bundle of fibres passes towards the angle of the mouth. The middle constrictor also receives fibres from the stylo-pharyngeus. It arises from the deep surface of the hyoid bone between the